304 stainless steels are widely used for high temperature components such as boiler tubes in thermal power plants. Therefore, it is important to clarify creep damage evolution process under multiaxial stress states in assessment of creep damage for actual components. In this study, creep tests were performed by using smooth specimens and notched specimens having multiple round notches with notch tip radius of 0.5mm(R0.5) and 2.0mm(R2.0) on SUS304 steel. Creep rupture times of the notched specimens were longer than those of the smooth specimens, and those of R0.5 were longer than those of R2.0. Creep damaged specimens were produced by interrupting the creep tests. Higher void number density was observed in the creep damaged smooth specimens compared with that of the CrMoV forging steel. The void number density takes the maximum value at notch root surface in R0.5, and decreased rapidly toward center of the specimen. On the other hand, distribution of the void number density almost uniform with a scatter of the values from notch root surface to center of the specimen in R2.0. Stresses and accumulated creep strain distributions at the notch root sections were clarified by finite element creep analysis. It was indicated that the distribution of the void number density depends not only on the maximum principal stress but also on accumulated creep strain. Then, a void number density prediction equation as a function of an axial stress and creep strain rate was derived. Increase of void number densities with time in the smooth and notched specimens were well predicted by using the prediction equation.
The long term creep degradation mechanism and the feasibility of creep damage analysis by means of hardness method have been evaluated for γ’-Ni3(Al,Ti) precipitation strengthened wrought superalloy, TOS1X-2, developed for 700°C class Advanced USC steam turbine rotor material. EBSD quantitative analysis of crept specimens suggested that creep deformation occurred at both grain boundary and grain interior. Very fine particles of γ’ phase at grain interior showed Ostwald type ripening in accordance with LSW theory, and PFZ appeared at grain boundary in crept portion. The linear relationship between hardness and γ’ precipitation density suggested that the softening found at simple aged condition is the result of the change in γ’ precipitation strengthening, which follows Orowan’s dislocation by-pass model. Also the relationship between hardness and local creep strain suggested that the hardening occurred at creep aged condition is due to work hardening. The procedure of creep damage assessment for precipitation strengthened superalloy by hardness was established, by means of estimating the amount of local creep strain in stress concentrated portion.
Silane type surface penetrants were applied to young age mortar for the purpose of shortening the construction period when silane type surface penetrants were applied to the newly constructed concrete structure and its strength characteristics were investigated. As a result, when the silane type surface penetrants were applied to mortar with age of 7 days, slight increase in strength was observed compared with applying to 28 days of age or compared with the untethered mortar. In addition, in order to estimate this cause, mass change and pore diameter distribution were also measured. As a result, it was considered that the reason why the mortar strength increases at the age of young age was due to the curing effect with the internal water by applying silane type surface penetrants at young age. Therefore, it was considered that there were few problems of strength by applying silane type surface penetrants to the mortar at the age of young age.
This paper aims to clarify a crack length on W-EDMed (Wired Electric Discharge Machined) surface and show an estimation method for the surface crack length of an electric conductive zirconia ZrO2-WC.The surface crack length was estimated based on experimental fracture strength of ZrO2-WC specimens with the W-EDMed surface and the fracture dynamics model. Two other estimation methods were used in this study to validate the crack length. One of them gave a practical crack length defined by removing thickness of the W-EDMed surface that fracture strength recovers. The other method also gave practical crack length evaluated by adding residual crack length on the ground surface to the ground removal length. Both practical lengths were evaluated by clarifying effects of the ground removal length on the fracture strength. The estimated crack lengths were compared each other. It provided the surface crack length ranged over from 45.6μm to 55.6μm. An effectiveness method for prediction of the crack length was considered based on the experimental results. The results showed that the estimated crack length as W-EDMed surface was different from both practical crack lengths. This reason why the difference occurred is because the tensile residual stress may be generated and distributed on the W-EDMed surface. W-EDM process can make zirconia ceramics induce large stresses with repetition of cooling from high temperature and changing its volume caused by structural transitions. Removing the W-EDMed surface over 10-15µm length can disappear the tensile residual stress and to provide an accurate crack length on the W-EDMed surface. It can bring a useful estimation method for an accurate crack length.
This study deals with the development of the novel rotary-hydrothermal process for potassium niobate, in special monophase KNbO3, under mild hydrothermal conditions at lower synthetic temperatures for short synthetic time with using lower concentration of KOH solution. Potassium niobates were synthesized by the conventional hydrothermal process and novel rotary-hydrothermal process and the products were characterized by XRD and SEM observations. As a result, monophase KNbO3 was obtained at 180°C for 12h with using 7.5 M KOH solution by the rotary-hydrothermal process and the particle size for their monophase KNbO3 products was finer than one synthesized by the conventional hydrothermal process. Effect of rotary-hydrothermal process on the microstructure and morphologies for potassium niobate was discussed, compared to the conventional hydrothermal process.
In this study a multiscale numerical simulation was presented for multiferroic composite materials consisting of ferroelectric (FE) and ferromagnetic (FM) phases to design the microstructure and the material combination. An asymptotic homogenization theory was employed to estimate macroscopic homogenized material properties. We focused on three-type conventional microstructures, a polycrystalline random structure, a polycrystalline layered structure, and a single-crystalline layered structure. On the other hand, three typical materials, barium titanate, lead titanate and PZT, were utilized for FE phase. In addition, two materials, cobalt ferrite and Terfenol-D, were selected for FM phase. At first the influence of the volume fraction of FE phase on macroscopic homogenized material properties was investigated for every condition. The optimum volume fraction was found to maximize macroscopic magnetoelectric (ME) effect. The ME coefficient at the optimum volume fraction was compared among three-type microstructures and six-type material combinations. We discussed how to determine the microstructure, the material combination and the volume fraction to get the maximum ME effect.
CFRTP (Carbon Fiber Reinforced Thermoplastics) are expected to be used in the automobile parts due to their properties such as high specific strength and high specific stiffness in order to reduce the weight of car body. However, due to the expensive carbon fiber, the cost of CFRTP is high and its application to automobiles is limited. For mass-produced automobiles, a multi-material concept using a combination of dissimilar materials has been attracting attention. While the multi-material concept is often used to joint dissimilar materials, such as composite materials, high tensile strength steel, Al alloy and so on, the method of combining dissimilar material into one part is also expected. For the development of automotive parts, CAE technology is required and in order to apply multi-material concept to mass-produced automobiles, optimization method of materials and shape is necessary to be developed in the future. In this study, multi-material hat shaped members of CFRTP and aluminum alloy were molded by using hybrid molding method and their bending properties were evaluated. Their FEM analysis was also carried out and the relationship between material cost and mechanical properties were evaluated. When the surface of Al alloy is treated by electrolytic polishing, delaminating between Al alloy and CFRTP was suppressed and high stiffness multi-material hat shaped member can be obtained. The multi-material hat shaped member of CFRTP and Al alloy has superior specific stiffness as compared with molded products using only CFRTP for surface material, although the specific maximum bending load was lower.
We applied various ionic liquids (ILs) to wood to enhance its fire resistance. ILs were impregnated into the wood at room temperature under reduced pressure. Thermogravimetric and differential thermal analyzer (TG/DTA) was used to study the thermal property of the IL-treated wood. All IL-treated wood exhibited enhanced fire resistance as compared with untreated wood. In particular, the TG curves for the choline dihydrogenphosphate ([Choline]PO4)-treated wood and 1,3-dimethylimidazolium dimethylphosphate ([MMIM]DMP)-treated wood showed higher residual weights. Their DTA curves showed no prominent exothermic peak, indicating that they can achieve greater fire resistance. [MMIM]DMP-treated wood satisfies the standard of fire-resistant materials in the combustibility test on materials for train carriages.
The effect of initial microstructures of low-carbon steel on austenite formation behavior during intercritical annealing was investigated. Three types of hot-rolled sheet specimens with different microstructures were used; specimen P consisting of ferrite and pearlite, specimen B consisting of bainitic structures, and specimen M consisting of fully martensitic structures. After the hot rolling, these specimens were cold-rolled, and subsequently heated to target temperature, and then water-quenched to room temperature. The martensite and/or bainite fraction corresponds to the fraction of austenite during intercritical annealing since the austenite transforms into martensite and/or bainite during the cooling process. The austenite fraction in specimen M was larger than that in specimens P and B below 730 °C, whereas the order of specimens changed to P > B > M above 740 °C. Below 730 °C, austenite connected along the rolling direction was observed in specimens P and B, while the distribution of austenite in specimen M was uniform. In contrast, austenite was connected and elongated along the rolling direction in all the specimens above 740 °C. The nucleation and growth of austenite can proceed under local equilibrium in specimens P and B, whereas that can proceed under paraequilibrium in specimen M below 730 °C. Moreover, the austenite growth can progress under local equilibrium in all specimens above 740 °C.